<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Document</title>
    <style>
    /* 不改变元素的display居中 */
    body{
        text-align: center;
    }
    </style>
</head>
<body>
    <a href="">a</a> <br>
    <button>btn</button>
</body>
</html>